Osbeck Var Research Articles

Acridone alkaloids. VII. Constituents of Citrus sinensis Osbeck var. brasiliensis Tanaka. Isolation and characterization of three new acridone alkaloids, and a new coumarin.

Fractionation and chromatography of the acetone extract of the root bark of Citrus sinensis OSBECK var. brasiliensis TANAKA (Rutaceae) afforded three new acridone alkaloids namely citrusinie-I, -II and citbrasine and a new coumarin, ethylsuberenol. The structures of citrusinine-I, -II, and citbrasine, and ethylasuberenol were characterized as 1a, 2a, 3, and 6, respectively. Citracridone-I (4), suberenol (7), suberosin (8), crenulatin (9), xanthoxyletin (10), xanthyletin (11), nordentatin (12), elemol (13), and p-hydroquinone were also isolated.

Abscission of Citrus Leaf Explants

The question whether abscisic acid (ABA) induces cellulase and polygalacturonase activity and, hence, abscission directly or whether its action is mediated by C(2)H(4) was studied in citrus (Osbeck var. Shamouti) leaf explants using aminoethoxyvinyl glycine (AVG), an inhibitor of C(2)H(4) biosynthesis. ABA in concentrations of 10 micromolar and higher induced C(2)H(4) production and accelerated abscission. AVG inhibited C(2)H(4) formation, activity of cellulase and polygalacturonase, and abscission in ABA-treated explants. AVG did not inhibit the increase in the activity of the cell-wall degrading enzymes or abscission in a saturating level of externally supplied C(2)H(4). This indicates that the effect of AVG resulted from inhibition of the formation of endogenous ethylene. The data indicate that in citrus leaf explants the induction of the activity of cellulase and polygalacturonase and abscission by ABA is mediated by C(2)H(4).

Studies on Leaf Oils of Citrus Species

Leaf oils from 6 domestic citrus species were analysed by gas chromatography and 32 compounds were identified as constituents of one or more oils. Most components present were common to all 6 citrus leaf oils, but the percent composition of some components, i.e. β-pinene, limonene, β-phellandrene, γ-terpinene, p-cymene, p-α-dimethylstyrene, citronellal, linalool and thymol methyl ether, differed considerably from species to species. For ex-ample, γ-terpinene is a main component (36.5%) of Shiikuwasha (Citrus depressa Hayata), but is a trace in leaf oils from Kawabata-mikan (C. aurea Tanaka) and Otaheite-orange (C. limonia Osbeck var. otaitensis Tanaka). Yuzu (C. Junos Sieb. ex Tanaka) is characterized by relatively high contents of β-phellandrene (11.2%) and p-α-dimethylstyrene (6.7%), which are minor constituents in the other 5 citrus leaf oils. Otaheite-orange is character-ized by high contents of limonene (39.7%) and citronellal (10.0%).